An overcentre valve — also called a counterbalance valve — does two jobs at once. It holds a load against gravity when the control valve is centred, and it controls the descent when the operator lowers it, by metering the return oil so the load cannot run away.

The difference between an overcentre valve and a plain lock valve is the second job. A lock valve is open or shut. An overcentre valve opens progressively in proportion to pilot pressure, which is what gives smooth, controllable lowering of a boom or a raised platform.

This version bolts straight to the motor face. On a winch, an auger or any motor that can be driven by its own load, the overcentre valve stops the load running away the moment the operator eases off.

Mounting it on the motor rather than back at the valve bank is not just tidier — it means a failed hose cannot let the load drive the motor, because the holding element is downstream of the hose.

Pilot ratio and setting

Set the overcentre pressure at least 30 per cent above the maximum load-induced pressure. Set it too close and the valve will chatter or lower jerkily; set it far too high and it will not open properly and the function will feel dead.

Check the motor frame before ordering. OMP and OMS bolt patterns are not interchangeable. If unsure, measure the bolt spacing on the motor face and send it through.

Manufactured by CBF Hydraulic, Montecchio Maggiore, Italy.